Russian opposition leader Aleksei Navalny says he will no longer observe the terms of his house arrest and has cut off the ankle bracelet used by the authorities to monitor his movements.

In a post on his website on January 5, Navalny called his confinement to house arrest illegal, saying Russian law states that the restriction can only be ordered for suspects or defendants who have not yet been convicted.

Navalny, a prominent critic of President Vladimir Putin, was convicted of large-scale theft on December 30 after a politically charged trial and handed a suspended 3 1/2-year sentence.

"I am the only person in the history of Russian courts to be under house arrest after being sentenced," Navalny wrote.

He later told independent Dozhd TV that Russian law "clearly says that you cannot keep an individual under a house arrest once a verdict has been announced."

On his website, Navalny said he had no plans to travel far, saying his "need for movement" was limited to trips to and from his office and "leisure" with his wife and children.

But Navalny's defiant statement raised the stakes in his confrontation with Putin's government, which he has challenged for years by leading street protests, documenting high-level corruption allegations, and running for mayor of Moscow in 2013.

The electronic monitoring tag that Aleksei Navalny reportedly removed from his ankle on January 5.

Navalny told Dozhd that it was very important for authorities to hold him "in isolation" but that he planned to live like an "ordinary citizen."

But he also vowed to push ahead with his opposition activities, saying: "I'm going to do exactly what I used to."

Navalny, had already challenged his house arrest hours after his sentencing, when he attempted to attend an antigovernment rally outside the Kremlin in central Moscow.

He was detained by police en route and returned to his Moscow apartment.

Navalny, 38, is already serving a suspended five-year sentence on a separate 2013 theft conviction, and has been under house arrest since late February.

In the December 30 verdict, he and his brother, Oleg, were convicted of stealing about 31 million rubles ($520,000) from two companies through fraud.

Oleg Navalny was sentenced to 3 1/2 years in prison.

Both men pleaded not guilty, and Navalny contends that the cases against him are Kremlin-driven punishment for his opposition activities and anticorruption investigations targeting powerful officials.

Navalny and his supporters say that his brother, who is not an activist or political figure, is being used as a "hostage" to put pressure on Navalny.

On his website, Navalny said that neither he nor his brother have received a copy of the verdict, which was delivered hastily -- in a break with normal Russian court practice -- after the judge abruptly moved the sentencing date from January 15 to December 30.

He said that his brother, who was immediately taken into custody and placed in a jail, is being held illegally because he has not received a copy of the verdict.

The absence of a copy of a verdict also means that Navalny and his brother cannot appeal their verdicts.

Navalny called their predicament "completely nonsensical -- essentially, I am being locked up, not to mention my brother, who is being kept in a detention facility without a valid sentencing order."